title	issue
Preparation that shipping methods no longer require an availability rule to be valid as of version 6.6.0.0	NEXT-30858

Core

Deprecated availabilityRuleId in \Shopware\Core\Checkout\Shipping\ShippingMethodEntity because type can be nullable in v6.6.0. Also, it will be natively typed to enforce strict data type checking.
Deprecated \Shopware\Core\Checkout\Shipping\ShippingMethodEntity::getAvailabilityRuleId because return type can be nullable in 6.6.0.0.
Added null as a possible parameter for \Shopware\Core\Checkout\Shipping\ShippingMethodEntity::setAvailabilityRuleId.
Changed the following methods so that shipping methods without availability rule will always evaluate as valid in 6.6.0.0:
- \Shopware\Core\Checkout\Shipping\ShippingMethodCollection::filterByActiveRules
- \Shopware\Core\Checkout\Cart\Delivery\DeliveryValidator::validate
Deprecated Required flag for availability_rule_id in \Shopware\Core\Checkout\Shipping\ShippingMethodDefinition.
Deprecated \Shopware\Core\Framework\App\Lifecycle\Persister\ShippingMethodPersister::getAvailabilityRuleUuid without replacement.
Added a new Migration for 6.6.0.0 \Shopware\Core\Migration\V6_6\Migration1697788982ChangeColumnAvailabilityRuleIdFromShippingMethodToNullable so that the availability_rule_id column in the shipping_method table is NULL by default.

Next Major Version Changes

Type changed from string to be also nullable and will be natively typed to enforce strict data type checking.